Telegraph exchange system



April 1941- e. A. LOCKE ETAL 37. 4

TELEGRAPH EXCHANGE SYSTEI Filed June 7, 1930 s Sheets-Sheet 2 m s m UAW-III a. A. 1. 0 6/05 l-T s. K/NKEAD AT TOP/V5) Y T H April 1, 1941.

GA. LOCKE ETAL 2,237,154

TELEGRAPH EXCHANGE SYSTEIl Filed June 7, 1930 8 Sheets-Sheet 4 THROUGH OTHER Ill-Il I G.A.LOCKE HWENTORSF. $.K/NKEAD A T roklvsx Ap 1, 1941. cs. A. LQCKE arm. 1 TELEGRAPH EXCHANGE SYSTEI Filed June '7,

1.930 8 Sheets-Sheet 6 UH HUM.

WVENTORS G. A. LOG/(E ,l". SKIN/(710 4 rfanusr m Elmo 35 Eu e. A. LOCKE EI'AL TELEGRAPH EXCHANGE SYSTEII Filed June 7, 1930 8 Sheets- Sheet 7 [W E N TORS G.A.LOCKE By A F. $.K/NKEAD AT TORNEY April 1,1941. 6.- A. LO CKE ETAI. TELEGRAPH EXCHANGE SYSTEH Filed June '7 1930 a Sheets-Sheet INVENTORS KE F.. 5. K/NKEAD ATTORNEY Patented Apr. 1, 1941 UNITED STATES PATENT-OFFICE TELEGRAPH EXCHANGE SYSTEM George A. Locke, Glenwood, and Fullerton S. Kinkead, Brooklyn, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York,

N. Y., a corporation of New York Application June '1, 1930, Serial No. 459,684

124 Claims.

This invention relates to a printing telegraph exchange system by means of which connections may be established quickly and efliciently for communication purposes between any of a plurality of subscribers telegraph stations, and

further by means of which such connections are to remain thus established for more or less temporary intervals in accordance with the wishes of the subscribers.

In short, the invention aims to provide be- .tween subscribers telegraph stations the same type of service that is now provided between telephone stations. At the present time'any telephone user may obtain a connection with any other such user by' merely signaling the 15 operator. In a similar manner, the telegraph exchange system disclosed herein provides means whereby any telegraph station served by the exchange system may obtain connection with any other such station by merely signaling the operator at a central ofllce to which the telegraph station is connected.

Accordingly, a primary object of the present invention is to provide a flexible switching system for quickly establishing and tearing down communication circuits between any of a plurality of subscribers printing telegraph stationsor between a subscribers station and an operator's printer set located at a central oflice.

A feature of this invention lies in the means.

used to indicate to the operator the progress of the building up and tearing down of -a complete connection between subscribers. Another feature lies in a nondnterfering circuit which permits the telegraph circuit of only the first of several operators answering a signal to be connected. with the trunk or loop circuit over which the signal is being transmitted.

Another feature is a switching device for opening a communication circuit between subscribers and for establishing a connection between the operators printer set and either subscriber.

Another feature is the, provision of automatic v Other objects and features will appear in the subsequent detailed disclosure.

The telegraph exchange system broadly comprises a group of subscribers telegraph stations each connected to a given central office over an individual loop circuit with other groups of subscribers stations similarly connected to other central ofllces. Telegraph trunk circuits extend between the central offices in question and cord circuits are provided at each central ofllce for connecting any subscribers line with any other such line in the same office or for connecting a subscribers line to a trunk circuit for connection to a distant station.

Referring to the drawings:

Fig. 1' shows the circuit diagram of a subscribers loop circuit including the apparatus associated with the loopat the central oflice as well as at the subscribers station. This circuit is individual to each subscribers loop and includes suitable audible and visible indicating equipment.

' I Fig. 2 illustrates in schematic form a two-way repeater cord circuit. Connected to and/or forming a part of this cord circuit are shown several novel features of this invention. In Fig. 2 the relays I45, I18, l8l and I82 together with the lamp I21 and the alarnr'l83 are not individual to a cord circuit but are common to all the cord circuits of a position; relays ,4! and M and the devices controlled by them are common to all the positions in an exchange. I

Fig.3 shows a special circuit arrangement for the operators printer telegraph set with its associated key equipment for connecting the printer set with a cord circuit in the local position or in an adjacent operators position.

Fig. 4 illustrates schematically the supervisory operators printing telegraph set and the peg count monitoring circuit.

.Fig. 5 shows the circuit diagram of the toll line trunk circuit used in connecting two distant central ofllces.

Figs. 6 and 'I show different long line subscribers extension circuits. Fig. 8 shows in schematic form the essential elements of a complete telegraph exchange system embodying the features of the invention.

Figs. 9, 10, 11 and 12 show the link and ,cord

circuits associated with an observer operators circuit.

Fig. 13 shows a special type of jack for the cutoff alarm feature. v

Fig. 14 illustrates an out-of-order busy cord.

The numbers herein referred to in connection with Fig. 8 represent the numbers of the figures which are shown in detail in other circuit arrangements.

The telegraph exchange system shown in Fig. 8

comprises two central ofilces A and B located at some distance'from one another. Toll line trunk circuits Fig. connect oflices A and B. Each trunkcircult is shown having terminal repeater stations nearest the central oflice. 'A plurality of subscribers stations C, D, E, F and G are connected over individual loops to ofllce A. Similarly, subscribers stations 0, D, E, F and G are connected to oflice B. Long line subscribers D and E are shown connected to central oflices A'and B through extension circuits Fig. 6 and Figs. 7a and 7b, respectively. Long line extension circuits Fig. 6 and Figs. 7a and 7b are located usually at a telegraph repeater station and are only used to connect to a subscriber located at a great distance from the central ofllce. when a very long telegraph channel is utilized to connect the distant subscribers loop with a central oflice, Figs.

v The rectangles which are connected to Fig. 1

indicate the signaling and switching apparatus associated with the subscriber's loop circuits at the central oflices while the rectangles Fig. 5

. indicate similar apparatus for the trunk circuits.

Each central oflice is equipped with at least one position to which an operator's printer set is connected. A supervisor operators set Fig. 4, which is common to many positions, is shownconnected to operators set Fig. 3. Each position ata central oilice is equipped with a plurality of connecting two-way repeater cords Fig. 2 for establishing connections between the subscribers stations, subscribers stations and .trunk circuits, or between trunk circuits.

The manner of establishing a connection between local subscribers stations is shown for stations F and G, the connection'being established by connecting the repeater cord Fig. 2 between the jacks of the respectiveloop circuits.

'A trunked circuit connection between. subscribers located at distant central offices is indicated as extending between stations 0 and C of central ofllces A and B respectively. At oflice A connectingcord Fig. 2 extends between-the connecting jackfor station 0 and the connecting Jack of the toll trunk circuit Fig. 5. Similarly, at oflice B connecting cord Fig. 2 extends between the connecting jack for station C and the connecting jack of the :toll trunk circuit Fig. 5. A built-up connection between distant stations may be etsablished over several central oflices, in a similar manner, by using central oflice B as an intermediate oflice and connecting cord circuit nication path is traced over the tip wire only; the 7 ring side being used for supervision and control purposes. Local connection The explanation given above in connection with Fig. 8-i'urnishes a general picture of the exchange system operation as a whole. The various types of circuit connections will now be taken up in detail by first considering a local connection, i. e., a connection between two subscribers having loop circuits terminating in the same central ofiice. A connection of the type here contemplated is similar to that shown in Fig. 8 between stations at F and G.

Referring to Fig. 1 which showsthe subscribers loop circuit, the equipmentabove and to the left of line .XX is located at the subscriber's station'while the equipment below and to the right of line X-X is located at the central office. The equipment at the subscriber's station comprises a printing telegraph sending and receiving unit II, comprising a printer magnet I00,

a set of sending contacts III and a suitable motor equipped with a pair of contacts which will open by mechanical means when motor stop signals are sent. External of the printing telegraph set and also located at the subscribers station are switch I02 for starting the printer set motor, a stop or break key I03 for stopping the prniter set, and bell I04 whereby the central ofllce may signal the subscriber's station, a test key I05 for testing locally the printer set while the loop is arranged so that the operator can ring, a flash key I06 for signaling the operator at the central oflice andseveral relays, the functions of which will be explained.

At the central oflice the tip T of the loop circuit terminates in a jack ill. A line lamp H2 and an auxiliary bell III are associated with the equipment at the central ofllce whereby the subscriber may signal the operator. In addition, there are provided several relays, to be discussed, for operating the signaling circuits.

The repeater cord, which is necessary for establishing a connection between local subscribers lines is shown in Fig.2. This cord contains a connected by means of answering plug HI and calling plug I22. The repeater unit comprises a group of four polarized relays I23 to I26 inclusive, each having line and auxiliary windings interconnected in shunt. A detailed explanation of the operation of this repeater unit will not be given in this application since a repeater of this type is fully described in U. S. Patent No. 1,752,436 to F. S. Kinkead dated April 1, 1930 which disclosure is hereby made a part of this present specification as if fully included herein. Associated with plugs HI and I22 are signaling lamps I21 and I28 used for indicating to the operator the progress of a call. The manner of operation of the relays and their functionswill be described in detail later.

Fig. 3 shows the operators printer telegraph circuit I08 which is used for communicating with subscribers when establishing a connection. The operator's printer set is connected to jacks I02 and I03 by means of plugs I00 and ISI and then to the cord circuit of Fig. 2 through key I 90. An operator's telegraph printer circuit is provided for each operator's position. Located at each position are a plurality of cord circuits with which the printer circuit is associated through a looping arrangement on a set ofkeys, each cord circuit being provided with an individual key for connecthg that circuit with the operators printer circuit. Keys' I85 and I88 are shown located in the same operator's position as circuit I88. Key I84 "is shown in a position adjacent to I88 and to the left oi! it; key I81 is shown in the position adjacent to I88and to the right of it. Opera-;

tors circuit I88 is capable of answering subscribers signal over cord circuits located on adjacent positions through keys I84 and I81 in a manner to be hereinafter described. In a similar manner operators printer telegraph circuit I88 .to the right of I88 and adjacent to it is shown connected to key I81.

Having briefly discussed the various circuit elements involved in establishing a connection between local subscribers lines, the manner in ring R through the winding of relay H8, contact of key I85, one winding of relay I81, contact I8I of operator's, printer set, upper contact of key I85, normal break cont-act ofreiay I88, to ground 8. Assuming that the subscriber desires to initiate a call, start switch I82 will be pressed, which closes a circuit from one side of power supply circuit 8 through the winding of relay I88 to the other side of the power supply, causing relay I88 to operate. Relay I88, in operating, locks up through its lower contact, contact of stop key I83 to the motor control contacts 1 of the printer. In operating, relay I88 closes a path through its upper contact to start the motor for the printer set and also to operate relay I88 through the same circuit. a

The operation of relay I89 opens the bell ringer circuit over the tip T of the loop, removes ground from the ring side R of the loop and closes the T and R leads of the loop through the subscribers station set to operate relay H at the central oflice. This last circuit is traced from negative battery I2 at the central oflice through the lower break contacts of relay II8,- upper winding of relay I I5, tip side of jack H I, T of the loop, flash key I86 located at the subscribers station, make contact of relay I89, contact of key I85, sending contacts I8I of the printer set, one winding of relay I81, lower contact of key I85, winding of relay H8, R of loop, break contacts of relays H8 and H6 in the central oflice to ground I1. The operation of relay II5 completes a path to operate relay IIIi from'ground on the armature and contact of H5 to battery through the winding of relay H6. The operation of relay H6 in turn operates relay H8. This circuit is traced from ground on the lower make contact of relay I I6 through upper inner break contact ofrelay H8 through the winding of relay H8 to battery. In-

cidentally, relay H5 is kept from releasing when relay H6 operates by the substitution of positive battery I6 on the lower make contact of relay I I6 for ground I1. This positive battery over ring side R of the loop is -traced back over side T of theloop to negative battery I2 as mentioned hereinbefore. Relay H8, in operating. lights lamp H2 from battery on the upper make contact of H8 to ground through lamp II2 indicat-v ing to the operator that the subscriber is calling.

circuit by merely operating switch I3 to connect relay I28 to battery on the upper inner contact of relay H8. With thisarrangement, when relay H8 operates,.relay I28 will operate to close a circuit containing generator H in series with bell H3. The operation of relay H8 not only lights the line lamp but connects battery from the lower contact of relay H8 through the 'secondary winding of relay H8 to the sleeve of-Jack H4 to put a busy indication on the sleeve of Jack H4. The secondary winding of relay H8 is connected in opposition-to the primary winding and prevents relay H8 from operating.

The operator'at the central oilice answers the call by inserting answering plug I2I, Fig. 2, ol'

the cord circuit into jack H4 of the subscriber's line. This energizes relay H8 as hereinafter described and thus extinguishes the lamp H2. The operation of key I86, Fig. 3, associated with the cord circuit connects the operators printer telegraph set I88 to the loop circuit for communication with the subscribers printer. Upon inser- .tion of plug I2I in jack H4 a circuit is completed to operate relays I32 and I34 to ground from negativebattery I3I in the cord circuit through resistance A of the potentiometer comprising re sistances A and B through the winding of relay I32, lower outer break contact of relay I33,.

through the upper winding of relay I34 to the sleeve of plug I2I, sleeve of jack 4, primary windingof relay H8 tog'round, thus operating,

relays I32 and I34. Relay H8 will now operate. Although the circuit to operate relays I32 and I34 was completed through the winding of relay H8, it will be noted that relay H8 does not operate until polarized relay I34 operates. Relay H8 is designed not to operate on the small cur-.

rent supplied through the high resistance circuit previously traced. The operation of relay I34 causes the operation of relay I I8 on a path traced through the low resistance secondary winding of relay I34 and the low resistance windings of relays I33 and I35 to battery. Upon the operation of relay H8, the circuit path previously If desired, the operation of relay H8 may be used to operate relay H9 will be opened and relay H8 will release causing the extinguishment of line lamp H2. The operation of relay II8 transfers the ring side of. the loop circuit R from positive battery I6 on the make contact of relay H6 to the same positive battery through upper make contact of relay H8, through the'lower winding" of relay H5, break contact of relay H1 and ring contact of jack III. The operation of relay- I34 causes it to lock up from ground through the winding of relay H8, through the sleeve of jack H4, through the secondary winding and lower contact of relay I34, winding of relay I33, winding of relay I35 to battery, thus operating relays I33 and I35. The-operation of relay I33 applies ground from its upper inner armature through -the L resistance, lower inner. break contact of relay I38, upper contact of relay I31, lower break contact of relay I38, contact of relay 125, one winding each of: relays I23 and I24, contact of key I38, contact of conference jack I28, through a resistance M to negative volt battery. This causes the repeater in the cord circuit to close, thus making it possible for the operators set shown in Fig. 3 to be connected to the answering cord associated with key I86, upon the operation of this key to the home position.

The operation of relay I33 connects the tip of the plug I2I through the upper outer and lower inner make contacts of relay I33, break contact of relay I38, contact of relay I23, one winding each of relays m and mam side contact or key I", lead M. lower left Side and rightjside contacts gofkey- I93 (normal position), Fig. 8,-

lead 3 to negative battery, Fig. 2, through resistance AA. This negative battery on the tip of plug I2I completes a path over the tip of jack I I4, through the lower make contact of relay III,

upper winding of" relay Iii, contact of jack III and T of the loop, back over R of the loop, upper outer make contact of relay III, lower winding of relay II5, break contact of relay- Ill, jack III to positive battery I6. This circuit energizes both windings of relay I IS, the windings of which are wound diilerentially so as to oppose each other, causing the relay to release and in turn to release relay Ili.

The busy condition on sleeve of jack 4,

formerly obtained 'by battery iromthe lower make contact of relay 0, is replaced upon insertion of plug I2I and upon the release of relay I I9 by battery from the sleeve of the cord circuit. The operator connects her telegraph printer set to the cord circuit by operating key I",

which is associated with the cord circuit previously inserted in jack II4, to the "home position. This action connects the operator's printer in series with the answering side of the single line repeater, this side having been closed by theoperation of relay I33 as hereinbeiore described. Consequently, communication may now take place between the operator and the subscriber through the cord circuit and into theline to which the cord is connected. This circuit is traced from tip of answering plug I2I, upper and the normal break contact of key I30, to negative battery 41 thus operating relay I40. .Relay I40, in turn, operates relay I42 from battery through the operated contact of I40, winding of relay I42, sleeve of jack I93, plug. I9I, winding of printer magnet I44, plug I90, sleeve of jack I32,-to'

ground.

Under normal. conditions when the operators set is not connected to, a cord circuit the circuit through the A lead is opened.- The a mature oi" relay I40 is then held against its contact by a local biasing current and relay I43 is kept nals either received from the line or sent to the line from the printer keyboard.- Relay I43 also serves toindicateto an operator that a linehas plished will now be described. It a cord circuit on which a listening key is operated is used to answer a call which another operator has already answered the second cord circuit will not be con 'nected to the line due to a non-interfering feature of the cord circuit, which will be subsequently described. in which case the A lead will be opened, relay I42 released and relay I43 operated thus completing a circuit from battery I43, Fig. 2,

winding of relay I43, K lead, make contact of relay I43 in operators circuit, B lead, D lead, upper make contact of lrey I". .P lead, to ground on contact of relay I32 in the cord circuit. Relay 2 in the cord circuit will always operate when a cord is inserted in a line jack on a circuit from ground through relay I I8 Fig. 1 notwithstanding the fact that another cord is already inserted in the multiple of the particular line Jack. The operation of relay I45, Fig. 2 will close a circuit to lightlamp I21 as a visible indication to the operator.

. from battery through the lamp I21 to ground upon the contact of relay I45.

Referring now to the circuit condition which exists when the operator is the first to answer the subscriber's signal and is thereby connected with her set in series with the tip of the answering cord, .a circuit i traced from negative battery in the supervisor-operators circuit over Q lead, Fig. 4, operator set, Fig; 3, tip of cord circuit, Fig. 2, line jackcircuit, Fig. 1, lower make contact of relay II3, upper winding of relay I I5,

operated from battery throughthe normal break contact of relay I42, winding oi relayl43, sleeve of jack I93, plug I9I, winding of printer relay'I44, plug I90, to ground on sleeve I92 holdingoperated printer magnet I44. When the printer is not in use, magnet I44 is therefore held locked up, thus preventing a free whirling of the printing telegraph set. Printer magnet I44 is also held operated when the operators'printer set is in use and current is flowing in lead A. This current will overcome the biasing current of relay I40 and operate I40. This operation will move the armature of relay I40 from its contact I to its contact 4 operating relay I42, as previously described, and releasingrelay I43. The printer will now be under control 01' relay I40: Relay I42 is a slow release relay so that it will remain operated while relay I43 is following the-printersip.

jack III, tip of loop, flash key I06, make contact of relay I09, key I00, subscriber's printer set,

one winding of relay I01, key I05, winding of relay III, ring of loop, upper make contact of relay IIO, lower winding of relay II5, contact of relay ,l II, jack III, to positive battery I 6. Communication may now take place between the operator and the'subscriber. the printer set of Fig. 3 to send the word operator" or opr, which is typed up on the receiving unit I00 of the subscriber's printer. The sub- 'scriber their answers by operating-the sender unit IN to transmit to'the operators printer set information regarding the called subscriber's line.

The operator, having obtained the information (let us supposelthatthe call is toa local sub- I scriber to whom she has direct access, then connects plug I22 of the repeater cord in the. called subscriber's line. Both the calling and the called subscribers have line jack circuits and subscriber's station circuits similar to Fig. 1. The

- insertion of plug I22 into jack II4 of the called subscriber's line causes the operation of relay I I8 in the line jack circuit, Fig. 1, and the :operation of relays I33 and I48 in the cord circuit on'a path traced from battery through the windings of relays I43 and I36, in series, sleeve of calling plug elapse'before it releases and closes the tip of the cord circuit through its contacts. The reasonior this will be described in connection with a de- This circuit is traced The operator operates astral scriptlon of the toll line circuit. The release of relay I41 connects the tip of the calling plugsill through-upper make contact of relay I38, break 'contacts of relay I41, .lower inner make contact of relay I38, break contact of relay I31,-lower break contact of relay I38, make contact of'relay I25, one winding each of relays I23 and I24,- right side contact of split key I30, contact of tact oi relay I09, to ground 9. The operation of relay H8 in the line jack circuit will complete a circuit from positive battery I8, contact of jack III, contact of relay II1,,lower winding of relay H5, upper make contact of relay II 8, ring of loop,

. winding of relay IIO, key I05, one winding of relay I01, sending contacts IOI, key I05, normal break contact -I09 to ground 9, operating relay H5. The operation of relay II will operate relay II6, which in turn will operate relay I49 and light supervisory lamp I28 in the cord circuit on a path as follows; ground on the upper make contact of relay I I 8, through the winding of relay II1, ring of jack II4,-ring of plug I22, key I50, upper inner break contact of relay I39, winding of relay I49 to negative 130 volt battery thus operating relay I49. The operation of relay I49, in turn, completes a circuit to light lamp I28 from ground on the upper inner make contact of relay I49 to battery through lamp I28. Relay I49 in operating applies ground from a lower make contact to the repeater circuit to keep the communication path closed. This ground is traced from a lower make contact of relay I48, through the'contact of relay I25, one winding each of relays I23 and I24, key I30, contact of conference jack I29 to negative 130 volt battery. The operator now rings on the circuit by momentarily operating ringing key ISI. This applies battery to the winding of the polarized relay I52 causing it to operate over key I50 and the ring side of the cord which, it has been shown, has ground applied to it from relay I I 8 in the line before described. When relay I31 is operated,

cycle ringing current from the upper make contact of relay I31 is applied to the tipof the line to ring the subscriber's bell over a circuit traced from the upper inner contact of relay I31, lower inner make contact of relay I38, break contact ofrelay I41, upper outer make contact of relay conference jack I29, to negative 130 volt battery jack circuit. The operation of relay I52 energizes the primary winding of relay I38 on a circuit traced from ground on the contact of relay I 52 to battery through the lower winding of relay I38 thereby operating relay I 38. Relay I38 locks up from 130 volt negative battery through its upper winding and its upper inner make contact to the ring side of plug I22 which has ground from relay H8. The operation of relay I38 releases relay I49 extinguishing the calling cord lamp I28. The operation of relay I38 also lights guard lamp I53 from battery on the upper outer make contact of relay I 38 to ground through lamp I53. The same contact which lights the guard lamp I53 prepares a circuit for relay I31to be operated from an interrupted ground I54. This interrupted ground I54 operates relay I31 at intervals. When relay I38 is operated and relay I31 not operated during an interval, negative 130 volt battery is applied to the tip of the calling cord, thence to the tip of the subscribers line from 130 volt battery on the lower break contact of relay I31, lower inner make contact of relay I 38, tip of cord I22 andout over the line to the subscriber's bell at the station. ringing will continue to be applied to the line until the subscriber answers. While the ringing is continuing, relay H5 in the line jack circuit will chatter, but to prevent thischattering from affecting the supervisory guard lamp I53 in the cord circuit, relay II8 isdesigned as a slow-release relay which will not release while relay II5 chatters. When the subscriber does answer by depressing the start key I02 at the station set, the same relays will operate at the-station as described in connection with originating a call and ground will be removed from thering of the loop circuit; the bell circuit over the tip side of the loop will be opened and T and R of the loop will be closed through the sending and receiving circuits of the subscriber's printer. In the line jack circuit the closure of the subscribers loop will cause both windings of relay I I5 to become energized and cause relay I I5 to release for reasons hereinbefore described in connection with originating a call. The circuit which energizes the upper winding of relay II5 in the line jack circult is traced from negative'battery in the cord relay I31, contacts of relays I36 and I41 to the tip of plug I22 and out over the line circuit. The

release of relay I I5 will release relay II8 whichwill remove ground from the ring side of cord I22 I and thus release relay I38 and extinguish guard lamp I53. The tip of the calling cord circuit is restored to the repeater circuit and communication may now take place between subscribers through the repeater with the operator's set monitoring on the circuit.

The called subscriber may acknowledge the call in some way, as by typing his code number on his printer. This will be received on the printer sets of both the operator and the calling subscriber. The operator monitors on this connection until the parties are in satisfactory communication and then disconnects her set'from the circuit by restoring key I98 associated with the cord circuit to its normal position from its operated "home position, thus leaving her set free to answer other .calls. The circuit which previously was traced' from the "M". lead of the cord circuit through the operators circuit now is traced through the lower left and lower right side normally made contacts of key I98 to negative battery through resistance I AA in the cord circuit.

When the call is completed a disconnect signal may be sent by the subscriber by pressing stop key I03 which opens the locking'circuit for relay I08, causing it to release and thereby open the circuit of the power supply to the printer motor. Relay I09 will also release and the subscriber's station will return to normal and restore the condition of an open tip and grounded ring. Relay H5 in the line Jack circuit will now reoperate since the ring winding only of the relay'will be energized. Relay III; will now operate from the contact of relay II5 to applya ground to the ring of jack H4 and to the cord circuit. In

This alternate the case of a calling cord, relay I43 will operate and place a ground from its upper inner make contact to light the supervisory lamp I26. In the case of an answering cord, a circuit is traced from ground on the ring of cord I2l, normal break contacts of key I55, one winding of relay I56, winding of relay I51 to battery, operating relays I56 and I 51. Relay I 51 completes a circuit to light supervisory lamp I58 from battery through the lamp, upper make contact of relay I51, con- I tacts of key I55 to ground on the ring of plug I2I.

The operation of relay I56 closes the answering side of the repeater from ground on its lower make contact. The operator, upon noting the lighted lamps, disconnects the repeater cord from the jacks oi the calling and called subscribers lines thus restoring all equipment .to normal.

It should be noted that if the subscriber's printer set is of certain well known types in common use, the subscriber may send a disconnect signal to shut down not only her own set but also the distant subscribers set by sending two shift signals on her printer equipment. Certain mechanism located in the subscriber's printer (not shown in the drawings since the printer forms no part of this invention) acts to open the motor control contacts. The opening of the motor con trol contacts releases relay I08 and has the same eiTect as opening the stop key I 03.

Trunk circuit connection The establishment of a trunk circuit connection is somewhat different from that outlined above for a local connection. By reference to Fig.-8, it will be seen that a trunk circuit connection is one of the type indicated for connection oi a station C at central ofllce A and a station C at central oillce B. The stations desiring connection have loop circuits terminating in diffeient central oflices, so that a trunk circuit is required for completing the connection between stations.

.Theconnecting cord used for establishing a connection of this type is shown in Fig. 2 and is the same type as that previously discussed.

The circuit connection of one termination of a trunk circuit is shown in Fig. 5. It is only necessary to show the termination of the trunk circuit at one central ofllce since it is identically terminated at each office between which it extends.

Referring to the drawing of Fig. it will be noted that the equipment in box S is novel to the present invention whereas the terminal repeater units TR and TR (Fig. 4) comprise standard telegraph equipment which, of itself, is known in the art. As illustrated, a telegraph channel connects both terminal repe ters, each of the latter in turn being connec to central oilices A and B. The repeater unit may be of a known type such as disclosed in U. S. Patent 1,479,430, to J. M. Fell, dated January 1, 1924. Several repeaters may be used in tandem between the terminal repeater stations. Such case may occur when the length 01' line is very long. It is understood, of course, that metallic, open wire diflerential duplex, two way polar, or carrier telegraph repeaters may be used. U. S. Patent.

1,469,259 to B. P. Hamilton October 2, 1923, discloses a carrier telegraph arrangement which may be used in this circuit.

The call is initiated in the same manner as previously described for a local connection; Referring .to Fig. 1 the calling subscriber presses start key I02 to start the printer set motor at the calling station, and to signal the central onice. The operator at the central omce responds by connecting her set to the jack of 'the calling subscriber's line through a cord circuit and obtains the necessary information in regard to the called station.

It is to be noted, at this time, that relay I60 0 1, the toll line terminating equipment is normally operated on a circuit from positive battery in the telegraph repeater overthe tip of the circuit, then through the contact of service observing jack I6I, upper winding of relay I60, lower break contactof relay I62, back over the ring of the circuit to negative battery at the repeater. Relay I60, in turn, operates relay I63 from battery on the lower make contact of relay I60 to! ground through the winding of relay I63. Relay I64 is also operated on a circuit from battery on the lower make contact of relay I63 to ground through the winding of relay I64. Relays I60, I63 and IQkare, therefore, normally held up.

After the operator has received the number of the called subscriber and learned that it is necessary to complete the call over a toll line, she inserts the calling cord into a toll line jack indicated as idle by the idle line indicator. The idle line indicator is a circuit well known in the telephone art and is, therefore, not shown on the drawings, since those skilled in the art should readily understand its application to the circuits disclosed. When'calling plug I22 of the cord circuit is inserted in jack I65 a circuit is completed from ground on bank 1 of the selector wiper I, through'one winding of relay I62, sleeve of jack I 65, over the sleeve of plug I22, through windings of relays I36 and Ill in the cord circuit, to operate relays I36 and I66 in the cord circuit and relay I62 in the toll line circuit. Relay, I66 will then operate on a circuit from battery on the lead R of the repeater TR, lower make contact of relay I62 to ground through the winding of relay I63. As heretofore described, in connection with a local call, relay I36 in the cord circuit, in operating, releases relay I". Relay I" is designed to be slow in releasing and a short interval of time of the order of slightly less than one second will elapse before the relay finally'releases and closes the tip of the cord through to the repeater circuit TR; The interval of time during which the tip is kept open by slow release relay I" is utilized to cause a calling signal on the toll line which is automatically given when a calling plug is inserted in a line jack. The open tip caused by the insertion of plug I 22 causes relay I 60 in the toll circuit at the distant central cme "a" to release which in turn releases relay I63. The release of relay I63 also releases relay I60 at oince B. Relay I63 is designed as a slow release relay and the interval of time during which the tip of the cord circuit is kept open is made just long enough to allow relay I 63 to release. The

release of relays I60 and I63 at B will prepare a locking down circuit for relay I60 which may be traced from one side of the upper winding of relay I66 through the upper back contact of relay I60, upper back contact of relay I63, upper normal back contacts of relay I62 to the other side of the upper winding of relay I 60. Relay I 63 in releasing lights lamp I66 from battery on the lower break contact of relay I 63 through the lower break contact of relay I 63 to ground through lamp I66, thus lighting the line lamp at ofllce 13" indicating to the operator at thatoflice that omce A" is calling. The battery which lights line lamp I66 is also used to make the sleeve of the line jack I66 busy through the secondary winding of relay l62. The upper and lower windings of relay I62 are connected in opposition to prevent the operation of the relay on a circuit from ground 'onselector I. Relay I63 as heretofore mentioned, is a slow release relay so designed that slight pulses on the toll line will not give" a false call, also that'it will not be affected by printer signals or by a momentary withdrawal of the When slow release relay 1" in. the cord circuit finally releases, the tip of the cord is-closed through and relay lil'reoperates, in tum,* causing the reo'peration of relays I63 and I64; The remaining details of the toll line circuit follow in manner identical with .that outlined for ofllce battery on the'sleeve of the cord, through the winding of relay I62 to ground on selector I. Sleeve relays I34 and I33 in the cord circuit also operate and apply negativebattery 'to the tip of the cord. The operation of relay I62 will open the short circuit around the primary winding of relay I60 and will complete a circuit to cause current to flow through the secondary winding of relay I60. Relay -I60 will not'operate at-thistime, since it windings are difierenti-ally connected and the flow of current in the primary and secondary windings act to oppose one another. The operation oi relay I62 causes the operation of relay I68, on a circult from negative battery over the rim from the repeater TR, lower make contact of relay I62 to ground through the winding of relay I68. The operation of relay I68 extinguishes lamp I66 by opening its lighting circuit. The operator at B then answers from her printer. These printer signals will not affect relay I60 since fluctuations in current due to the signals passing through both windings of relay I60 will affect the windings equally thus keeping the relay unoperated. When, however, the operator at oilice A" replies, the circuit through the primary It will be noted that it the operator at 3" removes her plug from the incoming trunkline circuit before receiving signals from ofllce "A that lamp I66 at oijlice B will not be extin guished but will relight as an indication to the operator at B that the Incoming call has not been answered. Upon reception of signals over the trunk' from ,A,'lamp I66at 3" will be extinguished as described hereinbefore. Theoperator at central oflice B may then proceedin a similar manner to extend the call to central oflice C if the call'is intended for a subscriber to be reached over central oflice C rather'thanior one to be reached directly from central oilice B.

There is another signal transmitted over the toll line diflerent from the calling signal, and

that is the disconnect signal. 'There' are,however, two ways of restoring a trunk circuit to normal. j 1 r,

If the connection isset up as-previously described, an operator may simly pull her cord out ofthe toll line jack. This releases relay. I62 in the toll circuit which restoresthejring circuit to the tip, releasesrelay I66, which in turn releases relay I69. Relay I 60, I63 and,,I64 remain operated. In accordance with this mode of operation the operator takes cognizance of a single lighted lamp as an indication to disconnect atoll circuit.

This manner of restoring a trunkcircuit to normal is convenient and simple whenever a communication path is established over a single trunk circuit between' two terminating central oflice's. However, if' a built up communication 1 4 circuit is established through several central winding of relay I60 will be opened while ourrent will still flow in the secondary winding of relay I60, thus causing the operation of relay I60 at oflice B. Relay I60, in turn, operates relay I63 which applies battery to operate relay I64 A circuit is now closed to operate relay I69 from battery on the lower make contact of relay I63, primary winding of relay I69 to ground on the lower ou er make contact of relay I 68, thus operating relay I69 and locking it up over battery through its lower inner make contact and secondary winding. The operation of relay I69 opens the circuit through the secondary winding of relay I60-allowing relay I60 to follow the printer signals, Relays I63 and I64 will remain operated during the printer interval due to the slow release feature of relay I63.

Incidentally, at this point, it is well to bring out the fact that the insertion of the calling plug at originating oflice A causes the operation' of relays I62 and I66 at A as hereinbefore described. The open tip caused by the slow release relay I" in the cord circuit opens the operating path for relay I 60 at the originating oflicefA and relay I60 will release. However, since relay I63 is a slow release relay, a path is closed to operate relay I69, before 'relay I63 finally releases, on a circuit from battery on the lower break contacts of relay I63, winding of relay I69 to ground on lower outer make contact of ,relayI68. Relay I69 locks up over its own lower inner make contact. Relay I63 then finally releases and releases relay I64.

oflices and over several trunk circuits theoperator at the through or intermediate oflice will not receive any disconnect indication whenever an operator at .a terminating ofiicesimply pulls her cord out of the toll line jack. A ten-second disconnect signal is therefore provided for indicating to the operator at the through or inter-v mediate oiiice that a subscriber has disconnected. To send a ten second disconnect signal the operator at the central oflice which receives the calling subscribers disconnect signal depresses non-locking key I5I in the cord circuit which isconnected tothe toll line jack. This disconnect signal ,will automaticallyappear on all oilices connected to the communication circuit. The operation of the non-locking key will apply 24 volt negative battery to the ring side of plug I22. Current now flows over the ring side of plug I22 which couldnot flow before because negative 130 volt battery was applied to both ends of the circuit. Relay I10 will therefore op-,

crate on circuit fromZl30fvolt battery through its secondary winding, upper normalbreak contact of relay; "I, through the winding ofrelay I" to 24 volt negativebattery on the ring of the plug. 'Relay I10 will lock up over its primary winding and upper make contact to ground on selector I through .the winding of relay I62.

The operation of relay. I10 will remove the groundfrom its lower break contact. from the tenth contact of selector bank I}. The operator will now remove theplug from the toll line jack circuit. Relays I60, I63 and I6! will release since the removal of the plug opens the tip of the tollline circuit and releasesrelay Ill and relay 'IIl. vRelays "I, I" and"! will remain opereted. A circuit is now closed for rotary magnet I" through the break contact of relay I, make contacts of relays I and I" tobattery. Rotary magnet Ill will be stepped around by contact to light lamp III whenever relay I opinterrupted ground I'll at'the rate of one step per second, which is the rate of interruption for I13. When the wiper of selector Li reaches'the tenth contact the operating circuit for relays It! and III, which was heretofore closed, will now be opened, thus causing their release, in turn releasing relays I and I. When relay ill releases, battery over the tip of the loop from the repeater TR is reapplied to relay I" causing it to operate, in turn, operating relays I and I G4. Relay Ill, in releasing, applies ground from its lower outer break contact through the winding of "release relay" I" to battery through oil-normal contacts II, the left contacts of which have been closed and the right contacts opened due to the selector being off-normal. The selector will now return to normal; The circuit has, therefore, been opened for secon and then closed.

It will be noted that the tensecond disconnect signal may be transmitted over the answering cord also, by depressingnon-locking key I in the answering side of the cord circuit whenever the answering plug is inserted inthe toll line trunk circuit. This applies a 24-volt battery to the ring of the answering plug. Key I" however, will not be used for this purpose in the circuit description herein described.

The above description of the disconnect feature applies to the transmission of the disconnect signal. The reception of a disconnect signal over the toll'line is somewhat different.

To receive a disconnect signal, assume that 1 the line is opened at the distant end by the depression of the non-locking key and 'the removal of the plug from the trunk circuit. At

the near end relays I60, I63 and I will release but relays I, I and I" will remainoperated because the plug at the near end is still in the m applies ground- -from;it| upper inner make erates. In answering plug-ill is inserted in the toll line jackinstead of "plug III, as at the called ofiice, the interruptediground-will trace a path over the ring of cord III, key I, one windins of relay I"; winding of relay I" to battery operating relays I" andlil. Relay I" will lock up' on a circuit-traced from negative 130 volt battery, lead T, normal contacts of operator's key I, lead N,- lower inner make contacts of V relay I", one winding of relay I" to groundon the upper inner make contact'of relay I. The operation of relay lll connects supervisory lamp I" to the ring circuit through the upper make contact of relay ill, lighting lamp I". When the interrupted ground"! from the toll circuit flashes off for a slight interval, relay ill will release and then lock down on a path traced from 130 volt negative battery on the upper inner make contact of relay Ill, lower inner break contact of relay I" through the winding of relay It! to 130 volt negative battery on the other side of'the winding. Lamp it. will then be connected to an interrupted ground lllwhich will flash'OJi second on 0.5-second off on a path traced from the upper outer make contact of relay I". upper through lamp III. In the case of the answeringouter break contact of relay ill to battery P us, the "flashing will originate invthe cord circuit while in the case of the calling plug; the flashing'originates in the toll line circuit and is transmitted .to the cord lamp through the ring of the jack and plug.

Conference connection exchange system disclosed herein to establish tall line jackl. Rotary magnet ill will now operate. Relay I" in operating will operate" relay ill from battery on its lower make contact through the winding of relay ill to ground on bank 2. Inoperating, relay I'll will lock up on so its lower make contact to ground from the lower outer make contact of relay in. Relay ill in operating transfers the ring circuit of theplug, which traces a path through line-jack I65 and the windingof relay m, to interrupted ground "2 on the upper inner make contact of relay I'll. This'circuit will flash the lamp in the cord circuit over the ring of jack I at the rate of 60 flashes per minute. The circuit for the flashing lamp is traced from interrupted ground III in the toll circuit, ring of caliingplugi2! (assuming that plug 1221s in jackiii which will occur at thecalling oilice) key I", upper break contact of relay Ill. through the windLingof relay I" to connections which are common to. more than two subscribers stations. Such connections are termed "conference connections."

Conference connections may be established which involve any number of stations, local as well as distant stations. In such a case connections areextended over trunk circuits from the distant stations to the nearest omce at which the local stations terminate and the plurality of stations are interconnected in a common communication circuit at such omce. Finally, conference connections may be established involving. distant stations only. For this case individual trunk circuit connections are extended from a plurality of stations to an intermediate ofiice distant from all the stations, and the various lines are interconnected at such intermediate oilice.

Conference connections of either type mentioned above may be established by inserting the "answering" plug of an idle cord circuit into conference jack III of any cord circuit connected to a communication circuit. The calling plug of this idle cord may then be inserted into the line of the party who desires to be added to the communication circuit. In this manner, any number of idlecords may be utilized to add any number of additional parties by inserting'the answering plug of an idle cord'into a'conference Jack of any cord interconnected to the communication circuit (either the original cord circuit-or the added cord circuit) and thenconnecting the.

battery. operating relay I at intervals.- Relay (5 calling plug of this idle cord to'the line lack of another subscriber or trunk circuit connected to another subscriber.

The insertion of the answering plug of another cord circuit into conference jack I29 .Jconne'cts the tip circuit of the added cord in serieswith.

the tipof the first cord circuit. Relay I33 of the second cord will operate from ground on the sleeve of the conference jack of the first cord. Negative 130 volt battery is thus taken oil the tip of the first conference jack I29 and negative 10 battery for the first cord repeater issupplied from the second cord through the tip of the second cord over the operated contacts of relay I33 in the second cord, contact of relay I39, contact of relay I23, windings of relays I26 'and I28 1:0

negative 130 volt battery over the M lead, key I96 and S lead of the second cord. This action will then place the calling side of the first re peater in series with the answering side of the second repeater. Communication may then take place between all established connections through the repeater circuits of all cords. The ring circuit of the conference jack is so arranged that ii there is a disconnection on both answering and calling sides of the first cord circuit the cord lamp will light in the second cord circuit. This circuit is traced from ground over the lower outer make contacts of relays I49 and I5! in the first cord circuit to the ring of the conference Jack I29,'thence to the ring of the answering plug 0 inserted into jack I29. In this manner any number of disconnect signals may be lit in the answering plug circuit of the added cord circuits provided that a double disconnect signal is received in the cord circuit of the one into which the added cord is inserted.

s lit key feature direction places a short circuit on the contacts of relays I23 and I25 through the lower por-v tion of the key arrangement. The operators printer is norm-ally in the answering plug side of the cord circuit and the conference jack in the calling plug side of the cord circuit. key I30 is thrown to the answering position the Y operator's printer remains unchanged in the answering plug side of the cord circuit over a path traced from the M lead through the upper break contacts on the calling side of key I30 and out to the tip of the answering cord through the windings of relays I26 and I25, short circuit on key I30, and the tip of the answering plug through contacts on relays I39 and I33. The short circuit caused by the operation of key I30 is to 0 I96 with the A lead of operators printer set I89,

.and will also connect the P lead with the B lead" prevent the subscriber on the calling side from interfering with communication between the operator and the subscriber connected to the an-' swering plug which might occur if the calling subscriber operates hisprinter or sends a discon (i5 transmitted over a direct circuit connection to the subscriber.

Now if key I30 is thrown to the calling position the printer I88 is placed in the calling side of the cord circuit and the tip side of the conference jack I29 is transferred to the answering When side 01 the cord circuit. Similarly, the contacts of both relays I23 and I26 are again short circuited so that the subscriber in the answering side of the cord cannot interfere with the signals transmitted between the operator's printer and the subscriber in the calling side .of the line.- The operators path is now traced from the M lead, make contacts on the calling side of key I30,

windings of relays I24 and I 23, short circuit in key I30 and out over the tip of the calling cord through the contacts of relays I38, I31, I36

Printer key The purpose of a printer key is to connect the operator's printer set to the cord circuit. The key may be provided to permit an operator on a position adjacent to the one in which the cord is located to connect her set to that particular cord This feature is .otten desirable when an operator on a very busy position has used up all the cords in her position to connect subscribers and has need for more cords to answer other subscribers.- or when an operator on a position has been relieved from work, the operator on the adjacent position can thereby monitor in on some of the cords of the vacant position. The team 3 keys are so arranged that an operator may only team in on not mor than half the keys on an adjacent. position. The rest; of the keys in that adjacent pmition are arranged for teaming into another position.

A printer key is associated with each cord circuit. This key may or may nothave two positions. For a cord circuit which is associated only with one position the home" position only is used. Other cords, usually the cords located at both ends-of an operators printer position, are arranged so that they can be used in either the "home position or on the adjacent positionnearest that cord. Where a key is adapted to be used for two positions a Iteamf' side of the printer is provided for association with the adjacent operator's printer set. The printer keys in a position are connected in series with mak-e before break contacts, and are so arranged that in a normal position the cord circuit terminates to battery through leads connecting the cord circuit to the keys.

The details of the circuit condition involved in connecting operators printer set I88, Fig. 3, to the cord circuit associated with key I96 by throwing key I96 to the "home" position were described in connection with the building upof a local connection. Assuming that the operatorin the position adjacent to printer set I88 and to of printer set I89 over the right hand contacts of key I96. Leads R, s andT will not be affected since both sides of the key are identical in arrangement in regard to these leads. Operator V I89 may now answer the suhscriber in the same manner as described in connection with a local subscriber. Similarly, operator I'88 may answer a call on the cord associated with key I94 on the adjacent lei-t vposi-tion by'thr-owing key I to the right or "team position.

Operator's printer set I88 may-alsobe used to answer a call on its adjacent right .position by throwing key I'9I to the team position. This will connect the A and B leads of printer set I88 over a loop arrangement involving keys I94, I95, I98 and I91 in series to the M and P leads of the cord circuit associated with key I91.

Key I95 located in the local position may only be used to connect the local operator's printer set, in this case set I88, to its associated cord circuit, since the team feature is not wired into that particular key. Each position may thus be equipped with cord circuits having both the home" and team features or the home" feature only as considered desirable.

In accordance with the principles underlying this feature of the invention, the A and B leads of a printer set are wired only to'answer on several cords on an adjacent position and not all th cords on the adjacent position, otherwise the A and B leads of the various printer sets would be interconnected.

If two keys on one position are thrown at the same time to either the home position or the "team" position, the key to the left only will be connected to the printer set while'the key to the right will simply be closed through to battery and not interfere with the printer set or the line circuit to which the left key is connected. This is illustrated in the drawing of Fig. 3 for the home conditions only. Assuming that keys I95 and I98 are both thrown at the same time to the home position, the cord circuit associated with key I95 will be connected to the printer set while the M lead of key I88 will be connected to battery over the contacts of key I95 to the S lead of the cord circuit associated with key I95. Since these same principles apply to the team condition it is not considered necessary to illushate this condition in the drawings and so multiply the number of figures necessary to illustrate this invention.

- Non-interference feature The non-interference feature is incorporated in the cord circuit and permits only the first of several operators inserting a cord in a line jack circuit to obtain proper connection with the subscriber. Returning now to the circuit condition when an operator inserts her answering plug .I2I into a line jack to answer a calling subscriber, a circuit is completed from ground in the line jack circuit through the 200 ohm winding of relay I I8, sleeve of jack 4 and plug I2I, 80 ohm winding oifv relay I34, lower break contact of relay I33, winding of relay I32 through a 1000 ohm resistance to a potentiometer made up of resistances A and B of 65 ohms and 135 ohms respectively. If

this cord is the first to complete the sleeve circuit, then the point of the potentiometer will be negative with respect to the sleeve due to negative battery I3I. Re1ay134 will therefore operate and lock up through its secondary 3.5 ohm winding as hereinbefore described. If another.

cord has preceded this particular cord into the multiple of the calling line, relays I34, I33 and I35 of thefirst cord will be connected to the sleeve circuit and operated. The sleeve of the first cord will then be connected to a 24 volt battery through the 3.5 ohm secondary winding of relay I34, in

series with the ohm winding of relay I33 and the 2.5 ohm winding of relay I35 makings. total of 56.0 ohms. Therefore, the sleeve of the line jack will be at a more negative potential than the. sleeve of the plug of the second cord, 1. e., the

potentiometer of the second cord will be positive with respect to the sleeve, and relay I34 in the second cord circuit will not operate. It is to be understood, of course, that-relay. I32 in the sleeve of the cord circuit always operates-upon insertion of the cord in the line iack for the purpose of indicating a special busy condition to the oper-' the sleeve of jack II4 in the line jack circuit and the sleeve of jack I65 in the toll line circuit is to make the circuit busy for operators who desire to use the line at a multiple position where an incoming signal is not provided. This feature will be described subsequently.

B usy test and out of order busy battery from the lower make contact of relay I I9 in the line jack circuit. battery on the break contact of relay I63 in the toll line circuit as previously described, or positive battery from the presence of an out of order" busy'cord.

Before the operator inserts her cord into a called subscriber's line or into a toll line circuit she will touch the tip of the plug to the sleeve of the jack. The negative battery present on the sleeve of a line in operation will operate relay I18 (which is polarized to be operated by negative current only) in the cord circuit on a circuit I traced from ground through the winding of relay I18 through the tip of either the answering or calling plug to the sleeve of the jack. In operating relay I18 will apply ground to light lamp I21 as an indication to the operator that the line is busy. 4

If a line is out of order, an out of order busy cord as illustrated in 111g. 14 will be plugged up in a multiple appearance of that line. This cord will supply positive battery to the sleeves of the jacks of that line. when the operator touches the tip of the plug to the sleeve of the jack relay I8I (which is polarized to be operated by positive current only) will operate from ground through the winding of relay I8I to positive battery on the sleeve of the jack. Relay III, in operating, will operate relay I82 and light lamp I21 on a circuit from ground on the make contact of relay I8I, through the winding of relay I82 to battery through lamp I21, will close a circuit to vibrate a sounder. or buzzer I83 from a 20 cycle generator supply I84 through the buzzer to ground on themake contact of relay I82.

If a cord is plugged into an open line and the operators key associated with that cord thrown a circuit will be closed which will operate relay I45. This circuit is traced from battery through the winding of relay I45, K lead, make contact of relay I43, make contact of key I95, P lead to ground on the make contact of relay I32. The operation of the last circuit was described in connection with a. local subscriber's call. The operation of relay I45 will light lamp I21 indicating that the operator's set is in an open line circuit.

It will be noted that the tip of a plug will be disconnected from the-busy circuit upon operation of the sleeve relay in the cord circuit whenever that plug is inserted into a line jack.

Flashing recall A subscriber often has occasion to signal an The operation of relay I82 operator after'aconnectio'n has been established with the operator or with another subscriber. For this purpose flash key I06 is provided in the subscribers equipment at his station.

Returning now to the circuit condition which exists'when a subscriber is in communication with another subscriber, let us assume that a subscriber wishes to signal the operator to initiate another call. Non-locking flash key I06 at the andcause it to operate. Relay H in turn operates relay II6. As the upper armature of relay H6 is now connected to the ring of jack II4 through the winding of polarized relay H1, the

closure of the upper armature will connect ground to the ring 01 the plug inserted in jack H4. Assuming that an answering plug I2I is inserted in jack I I 4 a circuit is completed through relays I56 and I51 in the cord circuit causing them to operate from ground on the ring of plug I 2I, contacts of key I55, upper winding of relay I56, winding of relay I51 to negative 130 volt battery. Relay I56 locks up to ground from the upper inner make contact of relay I33, lower winding of relay I56, lower inner make contact of relay I56 to 130 volt battery through key I96 over the N and T leads. Relay I56, in operating, applies ground to the answering side of the repeater holding the balance of the cord circuit closed from its lower outer make contact, contact of relay I23 and windings of relays I25 and I26 to battery over the M and S leads. Relay I51, in operating, connects lamp I58 to the ring of the plug, lighting lamp I58 The release of flashing key I 06 closes the loop and removes ground from the ring, releasing relay I51 which locks in a released condition due to the application of negative 130' volt battery to the other side of its winding from its lower inner break contact and the upper inner make contact of relay I56. The answering lamp I58 is now connected to interrupted ground. I19-which flashes the lamp at the rate of 0.5 second on and 0.5 second off until the plug is pulled down or the operator throws key I96 to monitor in on the circuit thus releasing relay I56. I Assuming that calling plug I22 is in jack H4 and that the-called subscriber flashes key I06,

then the ground on the ring of jack H4 from relay H6 is applied to the ring of plug I22 then to the normal contacts of key I50, upper inner break contact of relay I38 to battery through the winding of relay I49 operating relay I49. In, op-

erating, relay I49 applies ground from its upper inner make contact to light lamp I28. Lamp 128 will only flash in accordance with the operations of flashing I06 at the called loca'l subscribers set.

v If a subscriber is connected through a toll line circuit then the operation of key I06 at the suboperator pressing key I50 in the calling side of the cord circuit which applies positive volt battery to the ring of plug I22. It will be noted that upon insertion of plug I22 in the line jack of the called party that relay H8 in the sleeve of the line jack circuit is operated. Also, thatrelay II5 operated from positive battery I6 through one winding of relay H5 to ground on the ring of the subscribers loop. Relay I I5, in turn, operates relay II6. Therefore, the application of 130 volt positive battery to the ring of the cord cir cuit will complete a path to operate polarized relay H1 in the line jack circuit. This patnis traced from ground on the upper make contact of relay I I6 through the winding'of relay II1 to the ring of Jack H4. Relay H1 is 'a polarized relay and the direction of current flow is usually such as to keep it unoperated. The operation of ,relay II1 will apply negative battery I2 from its lower make contact to'the ring of the subscribers loop instead of the usual positive battery I6. The reversal of polarity .on the ring side of the loop operates polar relay H0 at the subscribers station which, in operating, closes the circuit of relay I08 in the same manner as does start key I02 where pressed, and puts the station in an operating condition. The motor for the printer set is thus started and theunattended station key I50 at the central office may be released. The subscribers loop T and R will now be closed through the subscribers station set, relay H5 in the line jack circuit will release, and line lamp I28 in the cord circuit will be extinguished. The extinguisl'unent of lamp I29, after the release of key I50, makes known to the operator the fact that the unattended subscribers motor for the printer set has started. If the lamp I28 does not remain extinguished after the operator has released key I50, it will be an indication to the operator that the subscriber's loop 'has not been closed through the station circuit. Key I50 will then be reoperated'.

, Ringing on the answering cord When a subscribers station is in the disconnected position and it is desired to ring on the answering plug over the subscribers line jackthe answering ringing key I55 is depressed. This introduces relay I39 into the ring circuit and causes it to operate on a circuit traced from 24 volt negative battery from the lower contact of key I55, winding of relay I39 to ground on the ring of plug I2I and jack of the-line. The operation of relay I39 will apply ringing current from source 39 through the upper make contacts of relay I39-and the make contacts of relay I33 to the tip of the plugjand out to ring the bell at the subscribers station. Key I55 while depressed applies ground from its upper make contact to the answering side of the cord repeater holding the balance of the circuit closed.

It will be noted that the ringing on.the answering plug is caused by continual manual operation of key I55 while that on the calling plug is automatic after only one operation of, I

key I5I.-

Cord cut-of) alarm circuit The purpose of this feature is to provide a visible and audible signal when a cord is removed from a communication circuit before .a disconnect signal is received.

Referring again to the circuit condition in the cord circuit which exists when communication is taking place between two subscribers, it will benoted that relays I48, I36, I35, and I33 are operated and that relay m is unoperated. With key I86 thrown, which occurs when the operator first monitors in on the circuit, a path is completed to operate relay 48 from ground on the upper make contact of relay I35, through the upper make contact of relay I48, secondary winding of relay 48 to 130 volt negative battery over leads R and T and key I86. Relay 48, in operating, will lock up through its primary winding on a path from ground on the upper'inner make contacts of relays I33 and I86 (or either of the relays if only one cord is inserted in a jack) upper make contact of relay 48, primary winding, upper outer break contact of relay I48 to battery on upper inner break contact of relay I56. Now, if one or both cords are pulled down by mistake either or both the I85 and I48 relays will release. Consequently, a circuit will be closed to operate relay H from, battery through either lamp I58 or I28 depending upon which cord is pulled down, the lower break contacts of either relay I35 or I48, the lower make contact of relay 48 to ground through the winding -of relay 4|. In operating, relay M will open the operating path of relay 42 thus releasing relay 42 which is normally held operated through the contact of relay 4|. The release of relay 42 will close a path to light lamp 48 and operate relay 44 from battery on the break contact of relay 42 through lamp 48 to ground through the winding of relay 44. In operating, relay 44 will close a buzzer circuit to operate buzzer 45. Thus, the cord lamp associated with the plug which was pulled down will be lit, cut-oil? lamp 43 will be lit and cut-off alarm 45 will function. Relay 42 is made slow to release to prevent false opera: tion of the alarm under ordinary disconnect conditions. The alarm will operate and stay operated until the cord has been restored to its.

proper place or other steps taken to release the relay 4.4.

If, however, a disconnect signal is received on either cord due to the operation of either relay I56,or relay I48, the locking up path for relay 48 will be opened and relay 48 will release and the circuit to the supervisors cut-ofl alarm circuit will not be completed.

Another method of restoring the cut-off alarm circuit once it has been operated by the accidental removal of a cord is to place the cord into a special jack Fig. 13, which has ground on the tip, ring and sleeve of the jack. The ground on the sleeve and ring of this special jack will, when plugged into, operate the sleeve relays of the cord and also give the disconnect signal thus releasing the cut-oil alarm relay H and restoring the normal condition of the circuit.

Supervisor printer and peg count. monitoring circuit In Fig. 4, there is shown a supervisor operators printer set which is arranged to be connected to an operators printer set by a key furnished at the supervisors desk.

This circuit is located at a special desk and is for the purpose of monitoring on any desired 3) at the switchboard has answered the subscriber, it will be recalled, that negative battery 41 for the operator's printer setwas obtained over the 61" lead through the contacts of key I88 in Fig. 4. Assuming that the supervisor desires to monitor on the switchboard operator's printer, the supervisor will operate key I88 associated with the particular position upon which she wishes to monitor. This action will transfer the Q lead from negative battery 41 to the lower make contact of key I88, through the other keys associated with other positions, lower left break contact of key 48, then to upper right break contact of the same key, through one winding of relay 48, back over the upper left break contact of key 48, upper left make contact of key I88, upper right break contact of key 48, left make contact of key 48 to negative battery 58, operating relay 48 in the supervisor operator's printer circuit. It will be noted that the supervisors set may only receive signals over this circuit since the sending contacts of the supervisors printer are now short-circuited. This path istraced from the tip of jack 5I in the printer circult, upper make contact of key I88, upper left break contact of key 48, to the tip of Jack 52. The circuit for the supervisor's set is similar in construction to the circuit for the operator's printer set previously described. Relay 48 is normally held to its 5 contact by the biasing current through one of its windings. A closed circuit may be traced from battery on relay 48 through the break contacts of relay 54, sleeve of jack 5|, sleeve of cord 55, printer magnet 53, sleeve of plug 56, to ground on sleeve of jack 52, thus normally holding the printer magnet 58 operated. The operation of relay 48, when connected into a circuit,'operates relay 54 on a path traced from battery through make contact 4 of relay 48, winding of relay 54, sleeve of jack 5|, sleeve of plug 55,

, winding of magnet 53 to ground on sleeve of jack operator's position at the switchboard by throw- 52 and plug 58. Relay 54 is designed as a slow release relay so that it will remain operated while relay 48 is following either the received or sent line signal impulses.

When the printer is not in use magnet 58 is held locked up, thus preventing a free whirling oi. the printer set. When the printer is in use and relay 54 is operated the printer magnet 53 is under control of relay 48. The motor for the printer will run continuously when the printer switch is on.-

To provide means for checking the peg count, key I88 is so arranged that by one operation of the key all springs on the left and right side of the key as shown in the figure make contact. This will connect the peg count set of the supervisor in multiple with the peg count set of the operator. Each operator has an individual key 58 located at her position. Associated with key 58 are relays 51 and 58 and a register 58. At the supervisors desk is a duplicate set of relays II and 62 and a register 63,'also lamp 68. when the operator has received or answered a call, she presses key 55 which completes a circuit from ground on key 56, windingof relay 51, message register relay 58 to battery operating relays 51 and 58. Relay 51, in operating. places ground on its own winding to short-circuit itself. This ground also serves the additional purpose of'insuring the operation of relay 58. The latter relay, in operating, actuates register 58 which contains a record of all calls. Relay 51, in shortcircuiting itself, falls back and releases relay 58 and register 58. Relays 6| and 82 and register 

